Methods and apparatus for power allocation on a reverse link power control channel of a communication system

ABSTRACT

A method and apparatus that determines how much power to allocate to each of a plurality of reverse link power control (RLPC) Channels to be transmitted from a base station, based upon data rate control (DRC) messages transmitted to the base station. Historical information is used to determine the quality of the Forward Link over which the RLPC is to be transmitted. If the history of the DRCs received indicates that the remote station to which the RLPC Channel is to be directed has not transmitted a DRC recently, then the base station allocates power to the RLPC Channels based upon information provided to the base station in DRCs that were received by the base station, but that were directed to other base stations. Accordingly, the base station can allocate power among the RLPC Channels without having received explicit information as to the quality of the Forward Link between the base station and every remote station intended to receive the information on the RLPC Channels.

CROSS REFERENCE

[0001] This is a Continuation Application of co-pending U.S. applicationSer. No. 09/267,565, entitled “METHODS AND APPARATUS FOR POWERALLOCATION ON A REVERSE LINK POWER CONTROL CHANNEL OF A COMMUNICATIONSYSTEM”, filed Mar. 12, 1999, and assigned to the assignee of thepresent invention.

BACKGROUND OF THE INVENTION

[0002] 1. FIELD OF THE INVENTION

[0003] The present invention relates generally to mobile radio telephoneSystems. More specifically, the present invention relates to systems andmethods for controlling the amount of power that will be transmittedfrom a base station to a remote station in a communication system.

[0004] 2. DESCRIPTION OF THE RELATED ART

[0005] It has recently become more common to use spread spectrumtechniques, such as code division multiple access (CDMA) techniques, tocommunicate information over wireless communication systems. Forexample, CDMA techniques are in wide use for communications betweenstationary base stations and mobile cellular telephones in a cellulartelephone network. In accordance with CDMA techniques, several streamsof information, typically from different sources, are each encoded (or“Channelized”) using a different code. These codes allow the informationto be transmitted over the same frequency band (commonly referred to asa “CDMA channel”). Each such Channelized information stream is commonlyreferred to as a “Code Channel”.

[0006] It is presently well known that in order to minimize the amountof interference between Code Channels of a CDMA channel, the amount ofpower that is transmitted on each of the Code Channels must be carefullycontrolled. Furthermore, it is common for a single amplifier to beresponsible for transmitting the entire CDMA channel. When a singleamplifier is used to transmit an entire CDMA channel, the more powertransmitted in one Code Channel, the less power is available to theother Code Channels. This is because there is typically a limit on theamount of total output power that such an amplifier can provide withoutundesirably distorting the amplified signals. For at least thesereasons, it is important to properly allocate transmit power to eachCode Channel in the same CDMA channel.

[0007] In one system used primarily for transmitting information at highdata rates over a wireless communication link, all of the Code Channelsin one direction are used to provide parallel data paths for informationfrom a first end point to a second end point of the communication link.For example, information transmitted from a base station to oneparticular remote station is transmitted over all of the Code Channels.The transmission path in this direction is commonly referred to aseither the “Forward Link” or “Down Link”. In such a high data ratesystem, each Code Channel on the Forward Link is allocated approximatelythe same amount of power for transmission from the base station.Furthermore, transmissions to different remote stations are timemultiplexed. That is, during a first time slot, all of the Code Channelsof the CDMA Channel are allocated to transmitting information to a firstremote station. During a second time slot, all of the Code Channels ofthe CDMA Channel are allocated to transmitting information to a secondremote station. Additional time slots provide communication linksbetween the base station and other remote stations.

[0008] The data path by which information is transmitted from aparticular remote station to the base station is commonly referred toeither as the “Reverse Link” or the “Up Link”. In one high data ratesystem, the Code Channels of a Reverse Link are each allocated todifferent remote stations. The amount of power that is used to transmitthe information on the Reverse Link must be controlled to reduceinterference at the receiving base station between Code Channels of thesame CDMA channel.

[0009] Accordingly, portions of each Code Channel on the Forward Linkare reserved for transmitting power control information. The reservedportions of a particular Code Channel within one slot form a “ReverseLink Power Control (RLPC) Channel”. Each such RLPC Channel on theForward Link is associated with one remote station. The power controlinformation that is transmitted on a particular RLPC Channel is intendedto be received and used by one particular remote station to control thereverse link power transmitted by that particular remote station. Thepower control information assists in maintaining the output power fromeach remote station at a minimum level required for information to bereliably received from each remote station on the Reverse Link.

[0010]FIG. 1 is an illustration of the format of a Forward Link of oneparticular communication system. In the system shown in FIG. 1, aportion of each Code Channel forms a RLPC Channel over which reversepower control information is transmitted.

[0011]FIG. 1 shows the Forward Link 100 formatted in Code Channels 102.Two Code Channels 102 a and 102 b are explicitly shown in FIG. 1.However, in accordance with the format shown in FIG. 1, 32 Code Channelsare provided on the Forward Link CDMA channel. Each Code Channel isdivided into “Slots” 104. In a typical system, such as the one shown inFIG. 1, each Slot 104 in the Forward Link has a predetermined duration.Each Slot is assigned to a particular remote station. In the systemshown in FIG. 1, each Slot comprises 2048 “Chips”. A Chip is defined asa duration in time that is equal to the duration of one bit of the codeused to channelize the Code Channels. Each Slot 104 begins with a firstdata field 106 that is 464 Chips in length. A pilot field 108 followsthe first data field 106. The pilot field is 96 chips in length. Thepilot field 108, among other uses, allows the receiving device tosynchronize to the phase of the incoming Forward Link signals (whichinclude the pilot field 108 itself. A second data field 110 having alength of 464 Chips is then transmitted. A third data field 112 having alength of 400 Chips is transmitted next. Following the third data field112, a power control field 114 is transmitted. The first power controlfield 114 has a length of 64 Chips. Next, a second pilot field 116having a length of 96 Chips is transmitted, followed by a second powercontrol field 118 having a length of 64 Chips. The last field in theSlot 104 is a fourth data field 120 having a length of 400 Chips.

[0012] The power control fields 114, 118 within one Code Channel 102form one RLPC Channel. Accordingly, the RLPC Channel is “Embedded” inthe Data. Under most conditions, a determination can be made at the basestation as to whether more, less, or the same amount of power needs tobe transmitted over the Reverse Link transmitted from a remote station.The determination is made based on the strength of the signal receivedby the base station from a particular remote station.

[0013] Typically, when transmitting the Forward Link, the same amount ofpower is used to transmit each Code Channel in the CDMA channel. It isappropriate to transmit the Code Channels at the same power, since theData is essentially directed to one remote station. For the purposes ofthis description, “Data” is defined as information that is provided bythe communication system user, and does not include information that istransmitted between components of the system in order to manage and/orsupport system operations (such as overhead messages). However, sinceeach RLPC Channel is directed to a different remote station,transmitting each RLPC Channel of the CDMA channel at the same powerlevel means that some of the RLPC Channels will be transmitted at powerlevels that are either greater than or less than is required. This isbecause the amount of power that is required to transmit to a remotestation that is closer is less than the amount of power required totransmit to a remote station that is farther away. Accordingly, it canbe seen that transmitting all RLPC Channels at the same power level isundesirable for the following reason. There is an absolute maximum totalamount of power that can be transmitted by all of the RLPC Channelstaken together. Therefore, using more power than is required for someRLPC Channels means that other RLPC Channels will get less power thanmight otherwise be possible if the power were allocated based on theactual requirements of each RLPC Channel rather than being allocatedequally to all RLPC Channels. This could be problematic if the farthestremote station requires more power than 1/N, where N is the total numberof RLPC Channels. It should be noted that the amount of power “required”to “reliably” transmit information, as referred to herein, is the amountof power that is needed to ensure that the information can be decodedwith a predetermined error rate. The particular error rate depends uponthe particular application of the disclosed method and apparatus.

[0014] However, determining the amount of power that is required by eachRLPC Channel is difficult for some base stations from which transmissionof RLPC information would be desirable. This can be understood from thefollowing example. FIG. 2 is an illustration of a system including threebase stations 201, 203, 205 and four remote stations 207. Each remotestation 207 typically maintains a list (commonly referred to as the“Active Set”) of base stations from which the Forward Link 208 to thatremote station 207 may originate. However, the Forward Link 208 willonly originate from one of the base stations in the Active Set at anyone time. The transmission path 209, 211 between those base stations203, 205 that are not transmitting the Forward Link 208 to the remotestation 207 a typically has different loss characteristics than thetransmission path 213 between the base station 201 that is transmittingthe Forward Link 208 and the remote station 207 a. Since nothing isbeing transmitted to the remote station 207 a from the other basestations 203, 205 in the Active Set, it is not possible to characterizethe loss over the Forward Links 209, 211 between the other base stations203, 205 and the remote station 207 a. Nonetheless, the remote station207 a will be transmitting to the other base stations 203, 205.Therefore, it is desirable to have each base station 201, 203, 205 inthe Active Set send reverse link power control information to the remotestation 207 a so that the remote station will have information regardingthe amount of power to send if selected to transmit.

[0015] Therefore, a need currently exists for a method and apparatus todetermine the relative amount of power that should be used to transmitreverse link power control information from a base station that is inthe Active Set of a remote station, but which is not transmitting aForward Link signal to that remote station.

[0016] These problems and deficiencies are recognized and solved by thepresent invention in the manner described below.

SUMMARY OF THE INVENTION

[0017] The disclosed method and apparatus determines how much power toallocate to each of a plurality of reverse link power control (RLPC)Channels to be transmitted from a base station, based upon data ratecontrol (DRC) messages transmitted to the base station. However, sincebase stations transmit RLPC Channels to remote stations that have notnecessarily transmitted a DRC to the transmitting base station,historical information is used to determine the quality of the ForwardLink over which the RLPC is to be transmitted. It should be noted thatfor the purpose of this document, quality is directly proportional tothe amount of power required to reliably transmit a predetermined amountof information in a predetermined amount of time with a predeterminederror rate. If the history of the DRCs received indicates that theremote station to which the RLPC Channel is to be directed has nottransmitted a DRC directed to that base station recently, then the basestation allocates power to the RLPC Channels based upon informationprovided to the base station in DRCs that were received by the basestation, but that were directed to other base stations. Accordingly, thebase station can allocate power among the RLPC Channels without havingreceived explicit information as to the quality of the Forward Linkbetween the base station and every remote station intended to receivethe information on the RLPC Channels.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The features, objects and advantages of the present inventionwill become more apparent from the detailed description set forth belowwhen taken in conjunction with the drawings in which like referencecharacters identify like elements.

[0019]FIG. 1 is an illustration of the format of a Forward Link of oneparticular communication system.

[0020]FIG. 2 shows a communication system that includes seven stations.

[0021]FIGS. 3a-3 c describe the disclosed method and apparatus from theperspective of one base station.

[0022]FIG. 4 is a block diagram of a remote station in accordance withone embodiment of the disclosed apparatus.

[0023]FIG. 5 is a block diagram of a base station in accordance with oneembodiment of the disclosed apparatus.

DETAILED DESCRIPTION

[0024] The method and apparatus that is disclosed in this documentallows a first station (such as a base station within a communicationsystem) to determine how much power to allocate to each “Reverse LinkPower Control (RLPC) Channel” that is being transmitted by the firststation. For the purpose of this document, a RLPC Channel is defined asany portion of a communication path that is used to communicateinformation from a first station to a second station regarding theamount of power the receiving second station should transmit back to thefirst station. A “Forward Link” is defined as a communication linktransmitted from a first station to a second station. A “Reverse Link”is defined as the communication link transmitted from the second stationto the first station. A “Base Station” is defined as a fixedtransmitting and receiving station for interfacing a wirelesscommunications device to a wireline communications system. A “RemoteStation” is defined as a station that communicates with a Base Stationover a wireless link.

[0025]FIG. 2 shows a communication system that includes seven stations201, 203, 205, 207 a, 207 b, 207 c, 207 d. In accordance with oneembodiment of the disclosed method and apparatus, the first, second andthird stations 201, 203, 205 are Base Stations. The fourth, fifth,sixth, and seventh stations 207 are Remote Stations (such as a wirelesslocal loop telephone, a hand held telephone, a modem, a computerterminal, or another device or system used to originate information tobe transmitted over the communication system). It should be understoodthat the number of Remote Stations is typically much greater than thenumber of Base Stations. However, only four Remote Stations 207 areshown in FIG. 2 for the sake of simplicity. It should be understood thateach station may be either a Remote Station or a Base Station, dependingupon the type of communication system in which these stations are beingused.

[0026] The disclosed method and apparatus is described essentially inthe context of allocation of power among RLPC Channels. However, insystems in which the roles of the Forward and Reverse Links are reversedfrom that set forth in this description, the disclosed method andapparatus applies equally well to the allocation of power among “ForwardLink Power Control Channels”. Nonetheless, for ease and clarity, thedisclosed method and apparatus is described in the context of allocationof power to RLPC Channels transmitted in the Forward Link.

[0027] In accordance with one embodiment of the disclosed method andapparatus, multiple Remote Stations concurrently transmit Data over theReverse Link to one Base Station. This Data is transmitted from eachRemote Station to a Base Station on a separate Code Channel. Forexample, the four Remote Stations 207 may each be transmittinginformation over the Reverse Link to the Base Station 201.

[0028] In the context of one system for allocating power among RLPCChannels, a Base Station transmits Data on a Forward Link to one RemoteStation at a time. In addition, each Remote Station preferably receivesData from only one Base Station at a time. For the purposes of thisdescription, “Data” is defined as information that is provided by thecommunication system user, and does not include information that istransmitted between components of the system in order to manage and/orsupport system operations (such as overhead messages).

[0029] Each Remote Station maintains a “Set” (or list) of “Active” BaseStations (i.e., an “Active Set”). A Base Station is placed in the ActiveSet if that Base Station is transmitting a Forward Link that is beingreceived by the Remote Station 207 with at least a predetermined levelof quality. In one embodiment, the quality of the Forward Link isdetermined by the quality of portions 108, 116 of the Forward Link 100,referred to as the “Pilot Channel”. A Pilot Channel is preferably madeup of portions 108, 116 of the Forward Link that are used by a RemoteStation to determine the quality of the Forward Link and to determinethe relative phase of the information being received by a RemoteStation. In accordance with the embodiment of the disclosed method andapparatus shown in FIGS. 1 and 2, the Pilot Channel is transmitted ononly one Code Channel 102 a from among the Code Channels 102 in the CDMAchannel. Furthermore, the Pilot Channel is transmitted only during twofields 108, 116 of each Slot 104.

[0030] The quality of the Pilot Channel may be determined by measuring aratio of signal to noise, frequently referred to as“Carrier/Interference” or “C/I”. Such measurements of the quality of thePilot Channel are well known to those skilled in the art. The quality ofthe Pilot Channel can be used to determine the quality of the entireForward Link. It should be understood that the quality of the ForwardLink may be determined by any other means known, such as by measuringthe signal to noise ratio of a Forward Link “Traffic Channel” (i.e.,that portion of the Forward Link that carries the Data). Alternatively,any other portion of the Forward Link may be used to determine thequality of the Forward Link. However, since the Pilot Channel ismodulated in a predetermined manner, the Pilot Channel provides anappropriate channel for determining the quality of the Forward Link.Nonetheless, signal to noise ratio is only one parameter that can beused by the Remote Station to determine the quality of the Forward Link.Any other method for determining the quality of the Forward Link can beused in accordance with the disclosed method and apparatus.

[0031] If the quality of the Forward Link received by a Remote Stationis such that Data can be transmitted over the Forward Link at apredetermined data rate with a predetermined reliability, then thetransmitting Base Station may be placed in the Remote Station's ActiveSet. However, in accordance with one embodiment of the disclosed methodand apparatus, a Pilot Channel from a particular Base Station may bereceived by the Remote Station with sufficient quality and still not beadded to the Active Set. This may be true if there are a predeterminednumber of Active Base Stations already in the Active Set and the ActiveSet can only support the predetermined number of Active Base Stations.In the embodiment of the disclosed method and apparatus in which C/I isused to determine the quality of the Forward Link, the Remote Station207 calculates a data rate based upon the C/I of the pilot received fromthe selected Base Station. The data rate is calculated to result in Databeing received at the Remote Station with a predetermined reliability.It will be understood by those skilled in the art that the reliabilitywith which Data can be transmitted depends upon the quality of theForward Link (i.e., the C/I) and the data rate.

[0032] Since the Remote Station only receives data from one of the BaseStations in the Active Set at any one time, the Remote Station selectsone of the Base Stations in the Active Set to transmit data to theRemote Station. The selected Base Station 201 is preferably the BaseStation 201 from which the Remote Station 207 receives the best qualityForward Link (i.e., the Base Station transmitting the Forward Linkcapable of supporting the highest data rate). In accordance with oneembodiment of the disclosed method and apparatus, the rate at which theselected Base Station can reliably transmit Data to a particular RemoteStation is communicated to the selected Base Station by the particularRemote Station 207 over the Reverse Link 210. The data rate is encodedwith a unique code that indicates for which Base Station the data rateinformation is intended.

[0033] When the selected Base Station receives the data rateinformation, the selected Base Station uses this information todetermine the C/I of the pilot that was received by the transmittingRemote Station. In accordance with one embodiment of the disclosedmethod and apparatus, the method used by the selected Base Station tocalculate the C/I of the Forward Link transmitted from the data rate isthe inverse of the method used by the Remote Station to calculate thedata rate from the measured C/I of the Forward Link pilot signal.

[0034] The selected Base Station determines the amount of power toallocate to a particular RLPC Channel based upon the quality of theForward Link as determined by the Remote Station. In accordance with theembodiment shown in FIGS. 1 and 2, the Forward Link can support as manyRLPC Channels as there are Code Channels 102. Each such RLPC Channel isintended for a different Remote Station. The number of RLPC Channels tobe transmitted by a Base Station is equal to the number of RemoteStations that include that Base Station in their Active Set. Forexample, if only three Remote Stations 207 a, 207 b, 207 c have aparticular Base Station 201 in their Active Set, then the Base Station201 transmits a Forward Link 208 that includes three RLPC Channels, oneRLPC Channel intended for each of the three Remote Stations 207 a, 207b, 207 c that include that Base Station in the Active Set.

[0035] The Base Station also receives information over the Reverse Linkfrom each of these three Remote Stations 207 a, 207 b, 207 c.Accordingly, the receiving Base Station 201 must provide power controlinformation to each of the three Remote Stations 207 a, 207 b, 207 c.This information is provided in a power control message over the RLPCChannels. Each such RLPC Channel is transmitted over one Code Channelduring the two power control fields 114, 118 of each Slot. No power isallocated to the unused RLPC Channels (i.e., to the other Code Channelsduring the power control fields 114, 118). Therefore, if the ForwardLink uses a CDMA channel that includes 32 Code Channels, only three ofthe 32 Code Channels are required during the reverse link power controlfields 114, 118 (assuming that the Base Station is included in theActive Sets of only three Remote Stations). Accordingly, no power wouldbe transmitted on the other 29 Code Channels of the Forward Link. Thisallows the maximum amount of power to be allocated to the three RLPCChannels that are directed to Remote Stations 207 a, 207 b, 207 c thatinclude the Base Station 201 in their Active Set. Each Remote Station207 a, 207 b, 207 c determines which particular power control message isintended for that Remote Station based upon the particular Code Channel102 over which the message is sent (i.e., the particular Code Channel102 that is used to support the RLPC Channel).

[0036] It can be seen that the allocation of power among the RLPCChannels requires that the Base Station identify each Remote Stationthat includes the Base Station in the Active Set. In addition, the BaseStation must determine the quality of the RLPC Channel in order todetermine the amount of power to allocate to each of the RLPC Channels.In accordance with the disclosed method and apparatus, the RemoteStation transmits an overhead message over the Reverse Link thatindicates when a new Base Station has been added to the Active Set. ABase Station that is added to the Active Set of a Remote Station willreceive overhead messages, either directly from the Remote Station orthrough another Base Station which then communicates the information tothe Base Station that has been added. Therefore, a Base Station canmaintain a list of those Remote Stations that include that Base Stationin their Active Set.

[0037] However, each Remote Station preferably only transmitsinformation regarding the quality of one Forward Link. That is, a RemoteStation only transmits information regarding the Forward Link betweenthat Remote Station and the one Base Station that is currently selectedby that Remote Station to transmit data to that Remote Station. Forexample, assume the Active Set of the Remote Station 207 a includes thethree Base Stations 201, 203, and 205. Remote Station 207 a transmitsthe data rate at which that Remote Station 207 a can receive Data fromthe Base Station 201, assuming that the Forward Link between the BaseStation 201 and the Remote Station 207 a has a higher quality than theother two Forward Links 209, 211. This data rate information can be usedto determine the quality of the Forward Link 208 (and so the quality ofthe RLPC Channel). However, while the Base Stations 203, 205 receive thedata rate information transmitted from the Remote Station 207 a, thedata rate information is only relevant to the Forward Link 208 betweenthe select Base Station 201 and the Remote Station 207 a. Therefore, theother Base Stations 203, 205 in the Active Set have no information aboutthe current quality of the Forward Links 209, 211 between them and theRemote Station 207 a.

[0038] Rather than allocating power among the RLPC Channels eitherarbitrarily or equally, the disclosed method and apparatus useshistorical information to assist in determining the quality of each ofthe RLPC Channels to be transmitted.

[0039]FIGS. 3a-3 c are a flowchart of the steps performed in accordancewith one disclosed method for determining the amount of power toallocate to each RLPC Channel. The method illustrated in FIGS. 3a-3 c isperformed independently by each Base Station in a communication system.The steps of FIGS. 3a-3 c are described below from the perspective ofone Base Station 201.

[0040] For the purpose of this description, it will be assumed that theBase Station 201 is receiving Data from three Remote Stations 207 a, 207b, 207 c. In addition, it is assumed that the Active Set of these threeRemote Stations 207 a, 207 b, 207 c include the Base Station 201. TheBase Station 201 receives “Data Rate Control” (DRC) messages over aReverse Link 210 associated with the first Remote Station 207 a. TheBase Station 201 stores the received DRC messages in both a “Short List”and a “Long List”. In accordance with one method, the Short Listincludes the five most recently received DRC messages and the Long Listincludes the twenty most recently received DRC messages. It should beunderstood that in one embodiment of the disclosed method and apparatus,the Long List includes the five DRC messages stored in the Short List.However, in an alternative embodiment, the Long List includes only thosetwenty DRC messages that were received before receipt of the five DRCmessages stored in the Short List. In yet another alternative embodimentof the disclosed method and apparatus, any other number of DRC messagesmay be stored in the Long and Short Lists. However, it should be clearthat the number of DRC messages stored in the Short List should be lessthan the number stored in the Long List. Furthermore, it should beunderstood that the greater the number of messages stored, the lower thereliability of the information in the older stored messages due to theage of that information.

[0041] The Base Station 201 makes a power control (PC) decision for eachRemote Station. That is, the Base Station 201 determines whether theRemote Station 207 a is transmitting the Reverse Link with too much ortoo little power (STEP 301). In accordance with one disclosed method,this determination is based on the error rate of the Reverse Link 210.In another disclosed method, this determination is based upon a C/Imeasurement of the Reverse Link. Those skilled in the art willunderstand that there are many other ways in which the Base Station candetermine whether the Remote Station has transmitted the informationover the Reverse Link with an appropriate amount of power to be reliablyreceived by the Base Station, but without using more power than isrequired. Accordingly, any known means may be used for making thisdetermination in accordance with the disclosed method and apparatus.

[0042] If the power that is being sent on the Reverse Link 210 isappropriate, (STEP 302), then no power is allocated to the RLPC Channelassociated with the Remote Station 207 a from which the Reverse Link 210originated (STEP 304). The power is appropriate if the Base Station 201determines that the power level of the Reverse link should not beadjusted. This condition is referred to as an “Erasure”. If the BaseStation determines that the Remote Station is transmitting with eithertoo little, or too much power, then a change in the amount of power isrequired on the Reverse Link 210 (i.e., an erasure does not occur) (STEP302). In such a case, the Base Station 201 determines whether the mostrecently received data rate control message (i.e., the “Current” DRCmessage) is “Valid” from the Remote Station 207 a. A DRC is consideredto be Valid if the DRC message content is received by the receiving BaseStation with a predetermined level of assurance in the accuracy of themessage content. The Base Station 207 a also determines whether theCurrent DRC message is “Directed” to the Base Station 201 (STEP 306).The DRC message is Directed to a particular Base Station if the DRCmessage provides information about the rate at which the transmittingRemote Station can receive information from that Base Station. Theinformation may be provided in any manner, such as a measure of thequality of the Forward Link, or the actual data rate that can besupported by the Forward link. It should be noted that in accordancewith one embodiment of the disclosed method and apparatus, each RemoteStation transmits DRC messages at a predetermined rate. Each DRC messageindicates the Remote Station from which the DRC message came. If a DRCmessage is Valid and Directed to the Base Station that receives that DRCmessage during a first period of time, then the DRC message is arelatively good indication of the quality of the Forward Link betweenthe Remote Station that transmitted the DRC message and the Base Stationthat received the message. If a DRC message which is transmitted duringa second time period is either not received as Valid by the Base Station201, or is not directed to the Base Station 201, then there is no way todetermine the quality of the Forward Link during that second period oftime.

[0043] Therefore, if the Current DRC message is Valid and Directed tothe Base Station 201, then the Base Station 201 uses the content of thatmessage to determine the quality (e.g., the C/I) of the Forward Link 208(STEP 308). In accordance with one embodiment of the disclosed methodand apparatus, the quality determination is based on the data rate thatis being requested by the Remote Station 207 a. The Base Station 201uses the inverse of the process used by the Remote Station 207 a todetermine the data rate from the C/I of the Pilot Channel of the ForwardLink 208. In addition, the Base Station 201 identifies the qualitydetermination of the Forward Link 208 as being “Reliable” (STEP 308).The quality determination is identified as being Reliable due to thefact that the DRC message was both Valid and Directed to the BaseStation 201.

[0044] Once the Base Station 201 has established a quality value for theForward Link 208, the Base Station 201 checks whether the quality of theForward Links 215, 217 to each other Remote Station 207 b, 207 c thatinclude the Remote Station 201 in the Active Set has been determined(STEP 342) (see FIG. 3c). As noted above, DRC messages are transmittedon each Reverse Link associated with a RLPC Channel. That is, DRCmessages are transmitted by each of the three Remote Stations 207 a, 207b, 207 c that include the Base Station 201 in the Active Set. If theBase Station 201 has not yet determined the quality of all three ForwardLinks 208, 215, 217, then the Base Station 201 continues the process atSTEP 301 in order to determine the quality of the next Forward Link(STEP 344). Once the quality of each Forward Link 208, 215, 217associated with each RLPC Channel has been determined, the Base Station201 allocates power to each RLPC Channel based on the qualitydeterminations and the reliability of those determinations, as will bedescribed in greater detail below.

[0045] If the Current DRC message is either invalid or not Directed tothe Base Station 201 (STEP 306), then in accordance with one embodimentof the disclosed method and apparatus, the Base Station gets the DRCmessages stored on the Short List (STEP 310). A determination is made asto whether the any of the most recent DRC messages were Directed to theBase Station 201 from the Remote Station 207 a (STEP 312). If at leastone Valid DRC message on the Short List is Directed to Base Station 201,then the Base Station 201 determines the quality (e.g., the C/I) of theForward Link 208 based on the value of the most recent Valid DRC messagedirected to the Base Station 201 and stored in the Short List (STEP314). As was the case in STEP 308, the Base Station 201 determines thatthe quality determination of the Forward Link is Reliable. Thisdetermination is made based on the results of STEP 312. However, in thecase of STEP 314, the DRC message is not the Current DRC message.Therefore, in accordance with one embodiment of the disclosed method andapparatus, the quality value is adjusted to compensate for the fact thatthe DRC message is not Current.

[0046] For example, in the case in which quality is expressed as a C/Ivalue, the C/I value is adjusted either up or down to compensate for thefact that the data rate information is not Current. In accordance withone embodiment, the C/I value associated with a Remote Station fromwhich no Current DRC message is available is adjusted to reflect agreater signal quality. The quality of the Forward Link will determinethe amount of power allocated to the RLPC Channel. Signals transmittedover lower quality links are transmitted with more power, while signalstransmitted over higher quality links are transmitted with less power.Therefore, adjusting the quality value to indicate a higher quality linkresults in less power being allocated to the RLPC Channel associatedwith the Remote Station 207 a from which no Current DRC message directedto that Base Station is available. This results in more power beingavailable for the RLPC Channel associated with the Remote Station fromwhich the Base Station has received a Current DRC message directed tothat Base Station.

[0047] Alternatively, since the Base Station 201 has received a DRCmessage that was Directed to the Base Station 201 relatively recently(as indicated by the fact that such a message is on the Short List) theBase Station 201 may adjust the quality value downward. Such anadjustment would result in more power being allocated to the RLPCChannel associated with that Remote Station 207 a. This is appropriateif there is a desire to increase the possibility that the RLPC Channelwill be reliably received by the Remote Station 207 a. As noted above,there is a limited amount of total power available to transmit all ofthe RLPC Channels. Therefore, increasing the amount of power with whicha RLPC Channel is transmitted to one Remote Station, decreases theamount of power that is available to transmit RLPC Channels to the otherRemote Stations.

[0048] In yet another embodiment of the disclosed method and apparatus,the Base Station 201 does not adjust the quality determination at all.By not adjusting the quality determination, an assumption is made thatthe benefits of providing more power to those RLPC Channels for whichthe quality is well known, is offset by the desire to provide a measureof reliability for the transmission of those RLPC Channels for which thequality is not as well known.

[0049] Having determined a quality value for the Forward Link 208 inSTEP 314, the Base Station 201 checks whether the quality of all of theForward Links has been determined (STEP 342) and if not, the processreturns to STEP 301 (STEP 344).

[0050] If the Base Station 201 determines that none of the DRC messageson the Short List are Directed to the Base Station (STEP 312), then theBase Station 201 determines whether at least one Valid DRC message wasreceived within a predetermined amount of time (such as 400 millisecondsin one particular example of the disclosed method and apparatus). In oneembodiment of the disclosed method, a “DRC-LOCK bit” is set when a ValidDRC message arrives. The DRC-LOCK bit indicates that the Base Station201 has received a Valid DRC message over the Reverse Link 210 from aRemote Station within the predetermined period of time (STEP 316). Thepredetermined time period is preferably greater than the amount of timeover which DRC messages are stored in the Short List, and equal to theamount of time over which the DRC messages are stored in the Long List.It should be noted that the Base Station 201 may also determine whethera Valid DRC message was received by any other means. For example, adetermination can be made as to whether any Valid DRC messages arepresent in the Long List by inspection of the stored DRC messages.

[0051] Accordingly, if the Base Station 201 has received a Valid DRCmessages within a predetermined amount of time, then such messages willhave been stored on the Long List. The Base Station gets the DRCmessages from the Long List. If any of the DRC messages in the Long Listare Directed to the Base Station 201 (STEP 320), then in accordance withone embodiment of the disclosed method, the Base Station 201 calculatesthe average of the quality values from all of the DRC messages Directedto the Base Station 201. The Base Station then determines the quality(e.g., the C/I) of the Forward Link 208 based on the average of all ofthe DRC message values (STEP 322). As was the case in STEP 308, the BaseStation 201 identifies the quality determination of the Forward Link asReliable based on the determination made in STEP 320 and establishes avalue for the quality of the Forward Link (STEP 322).

[0052] Having determined the quality of the Forward Link 208, the BaseStation 201 checks whether the quality of all of the Forward Links hasbeen established (STEP 342) and if not, the process returns to STEP 301(STEP 344).

[0053] If a determination is made that no Valid DRC messages have beenreceived by the Base Station 201 within the predetermined period (STEP316), or that none of the DRC messages were Directed to the Base Station201 (STEP 320), then the Base Station 201 will attempt to determine thequality of the Forward Link based upon DRC messages that were notDirected to the Base Station 201. However, the Base Station 201 willconsider this quality determination to be “Unreliable” since it is basedon information that is not Directed to the Base Station 201.

[0054] Assuming that none of the DRC messages received by the BaseStation 201 were Directed to that Base Station 201 (as determined inSTEPs 316 or 320), then the Base Station 201 determines whether theCurrent DRC message is Valid (STEP 324). If the Current DRC message isValid, then the Base Station 201 establishes a quality value (such as aC/I value) for the Forward Link 208. One means by which that BaseStation 201 establishes a quality value is by performing the inverse ofthe operation performed by the Remote Station 207 a when that RemoteStation 207 a generated the Current DRC message. The quality value isthen modified to correct for the fact that the value is Unreliable.Alternatively, the value of the DRC message may be used directly (suchas by reference to a lookup table) to determine the quality of theForward Link 208.

[0055] In one embodiment of the disclosed method and apparatus, the BaseStation 201 takes into account that the Forward Link 212 from the BaseStation 203 to which the DRC messages are currently Directed has thehighest quality. That is, Base Stations 201, 205 to which the RemoteStation 207 a has not Directed DRC messages will have a Forward Linkthat has a lower quality than the Forward Link transmitted from the BaseStation 203 to which the Remote Station 207 a is directing DRC messages.This is because the Remote Station 207 a always directs the DRC messageto the Base Station having the highest quality Forward Link.

[0056] By performing the inverse of the operation performed by theRemote Station 207 a to generate the DRC message, the Base Station 201can determine the maximum quality of the Forward Link 208. Therefore,the Base Station 201 preferably determines that the quality of theForward Link 208 is lower than the quality of the Forward Link 212, asdetermined from the value of the Current DRC message (STEP 326).However, this determination is considered to be Unreliable, since thereis no way to know exactly how much lower the quality of the Forward Link208 will be.

[0057] In one embodiment of the disclosed method and apparatus, the BaseStation 201 determines how much to adjust the quality of the ForwardLink 208 by taking into account additional information. Examples of suchinformation include: (1) a stored table that cross references thelocation of the Remote Station 207 a to the quality of the Forward Link208, (2) historical information regarding the quality of the ForwardLink 208, and (3) other information that is indicative of the magnitudeof the difference between the quality of the Forward Link 211, 212 aboutwhich the information is relevant and the quality of the Forward Link208 transmitted by the Base Station 201.

[0058] Having determined the quality of the Forward Link 208, the BaseStation 201 checks whether the quality of all of the Forward Links hasbeen established (STEP 342). If not, the process returns to STEP 301(STEP 344).

[0059] If the Current DRC message is not Valid (STEP 324), then the BaseStation 201 searches through the stored values in the Short List toidentify the most recent Valid DRC message (STEP 328). If the Short Listincludes at least one Valid DRC message (STEP 330), then the BaseStation 201 determines the quality of the Forward Link 208 based on thevalue of this most recent DRC message from the Short List. This qualitydetermination is marked as being Unreliable (STEP 332) to indicate thatquality determination was not made with regard to the Forward Linktransmitted from that Base Station 201. Since the DRC message is notDirected to the Base Station 201, the quality determination is merelythe maximum quality, and not the actual quality of the Forward Link 208.In addition, since the value is not from the Current DRC message, thevalue is made even more Unreliable (i.e., may not even be a reliablemeasure of the maximum quality). Therefore, in accordance with oneembodiment of the disclosed method and apparatus, the value ispreferably modified to indicate that the quality of the Forward Link 208is less than the quality indicated by the value of the DRC message.

[0060] Having determined the quality of the Forward Link 208, the BaseStation 201 checks whether the quality of all of the Forward Links hasbeen established (STEP 342) and if not, the process returns to STEP 301(STEP 344).

[0061] If none of the DRC messages in the Short List were Valid (STEP330), then the Base Station 201 checks to see whether any of the valuesin the Long List are Valid (STEP 334). If the Base Station 201 has beenreceiving DRC messages, then the Base Station 201 reads the DRC messagesstored in the Long List (STEP 336). The Base Station 201 determines thequality of the Forward Link 208 based on the DRC messages that are Valid(STEP 338). However, if none of the DRC messages in the Long List havebeen directed to the Base Station 201, then in accordance with oneembodiment of the disclosed method and apparatus, the stored DRCmessages are taken together to indicate the average quality of theForward Link 208. Typically, when the DRC messages are both old and havenot been Directed to the Base Station 201, each individual DRC messagevalue has relatively little significance. This is especially true sincethe quality of the Forward Link 208 changes relatively quickly. Once theaverage value is determined, the quality of the Forward Link 208 can beestimated to be worse than this estimate, since none of these valueswere Directed to the Base Station 201. Therefore, the estimation ismarked as Unreliable (STEP 338).

[0062] Having determined the quality of the Forward Link 208, the BaseStation 201 checks whether the quality of all of the Forward Links hasbeen established (STEP 342). If not, the process returns to STEP 301(STEP 344).

[0063] If there are no Valid DRC messages in the Long List (STEP 334),then the Base Station 201 assumes the quality of the Forward Link 208 tobe a predetermined value (STEP 340). In one embodiment of the disclosedmethod and apparatus, the predetermined value is an average value takenover a longer period then is represented by the Long List.Alternatively, the value may be a parameter stored in the Base Stationand set by system considerations, such as topography, average quality ofthe Forward Link within an area of interest, etc.

[0064] Having determined the quality of the Forward Link 208, the BaseStation 201 checks whether the quality of all of the Forward Links hasbeen established (STEP 342). If not, the process returns to STEP 301(STEP 344).

[0065] In accordance with one embodiment of the disclosed method andapparatus, for each Forward Link 208, 215, 217 for which the qualitydetermination was considered to be Reliable, the C/I value will not befurther adjusted to compensate for reliability. That is, the C/I valuethat will be used by the Base Station 201 will be essentially equal tothe C/I value that was measured by the Remote Station 207 a. However, inaccordance with an alternative embodiment of the disclosed method andapparatus, the C/I value will be modified by a factor which is afunction of packet length, level of confidence on the prediction, fadingmargin, and other such factors that can affect the correlation betweenthe value and the actual quality of the Forward Link 208.

[0066] Upon determining a quality factor for each Forward Link, theamount of power that is to be allocated to each of the RLPC Channels isfirst divided among those RLPC Channels for which Reliable qualityinformation is available. This allocation is based upon the amount ofpower required in light of the quality of each such RLPC Channel (STEP346). Next, the total power that is to be allocated according to therequirements of all of the RLPC Channels for which Reliable informationis available is compared to the total power available for all of theRLPC Channels (STEP 348). If the amount of power required for all of theReliable RLPC Channels is more than the total power available, then theavailable power is divided among only those RLPC Channels for whichReliable quality information is available, based on the relative qualityof each such Reliable Channel (STEP 350). This introduces an equaldegradation among all RLPC Channels for which reliable qualityinformation is available.

[0067] If the amount of power required for each Reliable RLPC Channel isless than the total power available (STEP 348), then the remaining poweris divided among those RLPC Channels for which only Unreliable qualityinformation is available (STEP 352).

[0068] In the embodiment of the disclosed method and apparatus in whichthe measure of the quality of a Forward Link is the C/I value, thefollowing formula is used to determine the amount of power required totransmit the Forward Link (STEP 346):

A[i]=(E _(b) /N _(o))·PG ⁻¹·(1/CtoI[i])  equation (1)

[0069] where E_(b)/N_(o) is the energy per bit divided by the noise, PGis the processing gain due to the encoding of the information, andCtoI[i] is the sum of all C/I values for the particular RLPC Channel forwhich a Reliable C/I value has been determined, A[i] is the amount ofpower required to transmit the RLPC Channel for the RLPC Channel havingthe CtoI[i] value.

[0070] Once the values for each A[i] have been calculated (i.e., anoutput power level has been calculated for each Forward Link for whichreliable quality information is available), a check is made to ensurethat the total output power allocated to all of the RLPC Channels doesnot exceed the maximum that the Base Station 201 can transmit, takinginto account any additional power required in the RLPC Channels foroverhead (such as forward activity bits or other such overheadmessages).

[0071] If the total power allocated by equation (1) to the RLPC Channelsdirected to Remote Stations over Forward Links for which Reliablequality determinations can be made is greater than the amount of powerthat is available, then in accordance with one embodiment of thedisclosed method and apparatus, the power is allocated to those RLPCChannels for which a Reliable quality determination has been madeaccording to the following formula:

A[i]={(CtoI[i] ⁻)/Σ(CtoI[j] ⁻¹)}(1−P _(overhead))  equation (2)

[0072] where CtoI[i] is the C/I value of the Forward Link to the RemoteStation to which the RLPC Channel to be allocated power A[i] is directedand CtoI[j] is the sum of the C/I values of each of the other RLPCChannels for which Reliable C/I values have been determined. No power isallocated to RLPC Channels for which Unreliable quality determinationshave been made. Accordingly, the power is allocated among the RLPCChannels for which Reliable quality information is available inproportion to the quality of each such RLPC Channel.

[0073] If the total power allocated by equation (1) is less than theamount of power that is available, then in accordance with oneembodiment of the disclosed method and apparatus, the following formulais used to allocate the power among the RLPC Channels:

A[k]{(CtoI[k] ⁻¹)/Σ(CtoI[l] ⁻¹)}{(1 −P _(overhead))−ΣA[j]}  equation (3)

[0074] where CtoI[k] is determined to be an Unreliable C/I valuedetermined for the Forward Link to the Remote Station to which the RLPCChannel to be allocated power A[k] is directed, Σ(CtoI[l] is the sum ofthe other C/I values associated with the RLPC Channels for whichUnreliable C/I values have been determined, and ΣA[j] is the sum of theC/I values of each of the other RLPC Channels for which Reliable C/Ivalues have been determined. Accordingly, once the power allocated tothe RLPC Channels for which Reliable quality information is available,the remainder is allocated to the RLPC Channels for which onlyUnreliable quality information is available. The remaining power isallocated in proportion to the estimates of the quality of each RLPCChannels for which only Unreliable quality information is available.

[0075] In one embodiment of the disclosed method and apparatus, the C/Ivalue may be adjusted to compensate for a lack of Reliability in thedetermination of the C/I at the Remote Station 207 a, or to otherwisealter the allocation of power between RLPC Channels transmitted over theForward Link 208. It should be noted that both the quality of theForward Link, as well as the reliability of the quality determination,are used in determining how to allocate power among the RLPC Channels.It should also be noted that in accordance with one embodiment of thedisclosed method and apparatus, RLPC Channels are transmitted to all ofthe Remote Stations each Slot (each RLPC Channel is modulated onto aseparate Code Channel 102). Therefore, regardless of the particularRemote Station to which the forward channel is currently beingtransmitted, RLPC Channels will be included that are intended to bereceived by each of the Remote Stations to which the Base Station 201may transmit (i.e., each Remote Station that includes the Base Station201 in the Active Set).

[0076] It will be understood by those skilled in the art that thedisclosed method is preferably essentially implemented as an executablesoftware application that is executed by a programmable device. FIG. 4is a block diagram of a Remote Station 400 in accordance with oneembodiment of the disclosed apparatus. The Remote Station 400 includesan antenna 402, a radio frequency (RF) front end 404, a digital signalprocessor (DSP) 406, a general purpose processor 408, a memory device410, and user interfaces 412.

[0077] In accordance with the disclosed method and apparatus, theantenna 402 receives Forward Link signals from one or more BaseStations. The signals are appropriately amplified, filtered andotherwise processed by the RF front end 404. The output from the RFfront end 404 is then applied to the DSP 406. The DSP 406 decodes thereceived Forward Link signals. In addition, DSP 406 provides anindication as to the relative quality of the received Forward Link. Theindication of relative quality is stored in the memory 410. The GeneralPurpose Processor 408 is coupled to the DSP 406 and to the memory 410.The General Purpose Processor 408 reads the indications of relativequality from the memory 410 and determines the rate at which eachreceived Forward Link can support data, and determines which ForwardLink can support the highest data rate. Once the General PurposeProcessor 408 has selected the Forward Link that can support the highestdata rate, the General Purpose Processor 408 communicates the selectionto the DSP 406. The DSP 406 encodes and modulates the information in aDRC, together with any information from the user interface 412, into aReverse Link output signal that is provided to the RF front end 404. TheRF front end processes the Reverse Link output signal and couples theReverse Link output signal to the antenna for transmission to each BaseStation capable of receiving the signal.

[0078]FIG. 5 is a block diagram of a Base Station 500 in accordance withone embodiment of the disclosed apparatus. The Base Station 500 includesa transmitter, such as an antenna 502 and a radio frequency (RF) frontend 504. The Base Station 500 further includes a digital signalprocessor (DSP) 506, a general purpose processor 508, a memory device510, and a communication interfaces 512.

[0079] In accordance with the disclosed apparatus, the antenna 502receives Reverse Link signals that have been transmitted from nearbyRemote Stations 400. The antenna couples these received signals to an RFfront end 504 which filters and amplifies the signals. The signals arecoupled from the RF front end 504 to the DSP 506 and to the generalpurpose processor 508 for demodulation, decoding, further filtering,etc. Upon decoding DRCs from the received Reverse Link signals, the DSP506 stores the decoded DRC in the memory 510 in both the Short List andthe Long List. In addition, the DSP 506 determines whether each receivedReverse Link was transmitted from the Remote Station with too much ortoo little power. It should be noted that the Base station 500 typicallyreceives Reverse Link signals from more than one Remote Station 400 at atime.

[0080] The general purpose processor 508 then performs the process shownin FIGS. 3a-3 c. The general purpose processor 508 communicates to theDSP 506 the amount of power that should be allocated to each RLPCChannel. Based upon the allocation of power to each RLPC Channel, theDSP 506 modulates and encodes the Forward Link signals to be transmittedby the Base Station 500. The signal is coupled to the RF front end 504.The RF front end couples the signal the antenna 502 which transmits theForward Link signal to the Remote Stations.

[0081] The disclosed method and apparatus is provided to enable anyperson skilled in the art to make or use the present invention. Thevarious modifications to the disclosed method and apparatus will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofinventive faculty. Thus, the present invention is not intended to belimited to the methods and apparatuses shown herein but is to beaccorded the widest scope consistent with the claims set forth below.

What is claimed is:
 1. A method for allocating power among reverse linkpower control channels on a communications link between a first stationand a plurality of second stations, including the steps of: a)attempting to receive forward link quality information from each of theplurality of second stations; b) determining the relative quality of aplurality of reverse link power control channels, each such reverse linkpower control channel being associated with one of the plurality ofsecond stations, the determination being based upon the forward linkquality information received from the associated second stations; and c)allocating more power to a reverse link power control channel associatedwith a lower quality forward link than to a reverse link power controlchannel associated with a higher quality forward link.
 2. A method forallocating power to a power control channel which is embedded within adata channel, including the steps of: a) determining the amount of powerthat is required to reliably transmit information over the power controlchannel to each of a plurality of remote stations; b) allocating theamount of power required to transmit the power control channel to eachof the remote stations based upon the determined power requirements; c)allocating the amount of power required to transmit each data channelbased on the total number of data channels and the total availablepower, independent of the amount of power allocated to each powercontrol channel.
 3. A base station within a communication system,including: a) a receiver configured to receive forward link qualityinformation from each of a plurality of remote stations; b) a processor,coupled to the receiver, configured to: i) determine the relativequality of a plurality of reverse link power control channels, each suchreverse link power control channel being associated with one of theplurality of remote stations, the determination being based upon theforward link quality information received from the associated remotestations; and c) allocate more power to a reverse link power controlchannel associated with a lower quality forward link then to a reverselink power control channel associated with a higher quality forwardlink.
 4. A base station in which power is allocated to a power controlchannel which is embedded within a data channel, including: a) aprocessor configured to: i) determining the amount of power that isrequired to reliably transmit information over the power control channelto each of a plurality of remote stations; ii) allocate the amount ofpower required to transmit the power control channel to each of theremote stations based upon the determined power requirements; iii)allocate the amount of power required to transmit each data channelbased on the total number of data channels and the total availablepower, independent of the amount of power allocated to each powercontrol channel b) a transmitter, coupled to the processor, configuredto transmit the power control channels to each of the plurality ofremote stations at the allocated power levels.